8 2 THE P OP ULAR S CIENGE MONTHL Y. 



ber; from some plots the clovers and umbel lifers are banished alto- 

 gether, while in other cases they may be proportionately increased. 

 Even among the grasses the competition is very severe, and the result 

 in some cases is that all or nearly all have to give way to the cock's- 

 foot grass (Dactylu ccespitosa), the growth of which is so fostered by 

 certain manures as to cause it to overcome its fellows and remain mas- 

 ter of the situation. To the plots to which a mixed mineral manure, 

 consisting of salts of potash, soda, magnesia, and lime, is applied, but 

 little difference in the number of species is observable. On the other 

 hand, manures containing ammonia salts, or nitrates, cause a great 

 diminution in the number of species living in the plot to which they 

 are applied. While the unmanui-ed plots furnish by weight about 60 

 per cent, of grasses, the remainder, consisting of plants of other fami- 

 lies, the plots to which admixture of mineral and nitrogenous manures 

 is added, contain as much as 95 per cent, of grasses, and these belong- 

 ing to a comparatively very few species. Salts of potash and lime, 

 which are comparatively inert as regards grasses, manifest their influ- 

 ence in increasing the vigor and the absolute numerical proportion of 

 the leguminous plants. 



The manner in which these results have been arrived at is worthy 

 of a short description in this place. 



Notes are taken at frequent intervals during the season of growth, 

 the appearance of the plants noted, their relative luxuriance observed, 

 and their comparative tendency to produce flower or stem and leaf, 

 the abundance of flowers, etc., etc. Root-growth is studied, and also 

 the character of the soil in the various plots, and the way in which 

 its texture and its capacity for holding or transmitting water are mod- 

 ified according to the manure applied. When the crop is cut from 

 each plot, its weight is estimated, and also the amount of dry produce. 

 In some cases chemical analysis is pushed further, and the ashes duly 

 examined. In addition to these no trifling observations, three " sepa- 

 rations " have been carried out at regular intervals. These separa- 

 tions consist in the picking out, from a sample of a certain weight 

 taken from each plot, every fragment of every species contained in 

 the sample. In this way the relative quantity and weight of each of 

 the different plants in the several samples are accurately determined, 

 and the proportion in the whole plot computed. The labor is enor- 

 mous ; but the results, when fully brought out, must be most impor- 

 tant, both as regards the scientific aspect of the question, the history 

 of the life-struggle between plants so circumstanced, and also as re- 

 gards the practical hints to be derived by tie cultivator. 



Some experiments of a somewhat similar character, and bearing 

 directly on the struggle for life among plants, have been made by Prof. 

 Hoffmann, of Giessen, and they are of such interest that we introduce 

 here a veiy condensed account of them, taken from the pages of the 

 Gardener's Chronicle, 1870, p. 664 



